SQL 查询入门

Python 中的数据库入门

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

SQL 语句

查询、插入、更新、删除数据
创建与修改数据

基础 SQL 查询

SELECT column_name FROM table_name

SELECT pop2008 FROM People
SELECT * FROM People

基础 SQL 查询

from sqlalchemy import create_engine

engine = create_engine('sqlite:///census_nyc.sqlite')

connection = engine.connect()

stmt = 'SELECT * FROM people'

result_proxy = connection.execute(stmt)

results = result_proxy.fetchall()

ResultProxy 与 ResultSet

result_proxy = connection.execute(stmt)

results = result_proxy.fetchall()

result_proxy 是 ResultProxy
results 是 ResultSet

处理 ResultSet

first_row = results[0]
print(first_row)

('Illinois', 'M', 0, 89600, 95012)

print(first_row.keys())

['state', 'sex', 'age', 'pop2000', 'pop2008']

print(first_row.state)

'Illinois'

用 SQLAlchemy 构建查询

以 Python 方式构建 SQL 语句
屏蔽不同数据库后端差异

SQLAlchemy 查询

from sqlalchemy import Table, MetaData
metadata = MetaData()

census = Table('census', metadata, autoload=True,
  autoload_with=engine)

stmt = select([census])

results = connection.execute(stmt).fetchall()

SQLAlchemy 的 select 语句

需要一个或多个表或列的列表
传入表将选取其中所有列

stmt = select([census])

print(stmt)

'SELECT * from CENSUS'

Passons à la pratique !

Python 中的数据库入门